As important as face masks are in our current pandemic-riddled world, they have a major impact on the environment. Now scientists have demonstrated a novel method for disposing of old masks – by using them to make low-cost, flexible and efficient batteries.

Personal protection equipment (PPE) is one of our most crucial defenses in the war against SARS-CoV-2, but unfortunately it needs to be disposable to provide maximum protection. That of course adds up to a huge burden of waste, with a 2020 study estimating that up to 129 billion face masks were used each month during the early stages of the pandemic. These end up in landfill, oceans and other environments, or are burned, giving off toxic gases.

To relieve this pressure, scientists are finding ways to recycle masks into useful things, such as road materials. And in that vein, a new study has now found that with the right treatment, they actually make fairly decent batteries.

First, the researchers disinfected the masks using ultrasound, then dipped them into an ink made of graphene. Next, the masks are compressed and heated to 140 °C (284 °F), forming conductive “pellets” that work as the electrodes of a battery. These are separated by an insulating layer that’s also made of old masks, then the whole thing is soaked in an electrolyte and finally covered in a protective shell that’s made of a different type of medical waste – drug blister packs.

Of course, cleaning up face masks is only part of the equation, and it wouldn’t be much help if the batteries weren’t any good. But they’re surprisingly effective, with the team claiming that they achieved an energy density of 99.7 watt-hours per kilogram (Wh/kg). That’s approaching the energy density of the ubiquitous lithium-ion battery, which ranges between 100 and 265 Wh/kg.

The researchers improved the battery even further by adding nanoparticles of a calcium-cobalt oxide perovskite to the electrodes. This more than doubled the energy density, bringing it up to a respectable 208 Wh/kg. The best-performing version of the battery retained 82 percent of its capacity after 1,500 cycles, and could deliver energy for more than 10 hours at a voltage up to 0.54 V.

The team says that these batteries have a number of other benefits too. Using waste products means they’re low-cost, and they can be made thin and flexible, and even disposable if need be (although that might undercut the original intention somewhat).

The research was published in the Journal of Energy Storage.

Source: National University of Science and Technology

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